Arched dam



March 6, 1934- c. c. TILLOTSON ARCHED DAM Filed June 18, 1930 INVENTOR Patented Mar. 6, 1934 UNlTED STATES PATENT OFFICE,

3 Claims.

The purpose of this invention is to increase the safety of arches and arched dams made of any material, and to decrease the amount of material required, thereby decreasing the cost.

The invention consists of a novel combination of hitherto known elements in structural and mechanical engineering, resulting in an arch or dam in which uncertainties as to stresses induced, and complications due to distortion in the structure, are replaced by certain simple and well defined stresses capable of exact determination.

The parts of this invention may be applied to arches used for any purpose, thoughthe drawing illustrating the invention shows in particular parts of single and multiple arch dams. The invention may be used in arched dams of either constant or variable radius, or of constant or variable angle of arch.

Referring to the drawing, Fig. 1 is a plan of a single arch; Fig. 2 is a plan showing two typical arches of a multiple arch; Fig. 3 is a plan, much enlarged, of an arch hinge; and Fig. 4 is a vertical section on the line IV-IV, Fig. 2.

All these figures are views of arches presumed to have vertical axes. The axis of the arch may also be inclined, or horizontal.

Fig. 1 shows the arch to be a hinged arch, consisting of two principal segments of arch, 1 and 2, separated by an intermediate hinge element 3, and supported against the thrust of the load above it by abutments 4 and 5.

This shows the two principal segments of the arch, 1 and 2, reinforced and stiffened, so as to prevent any deformation of the arch segments, by trussed frames 21 and 22, securely attached to the arch at all points of contact therewith, and suitably supported vertically.

This reinforcement may be of the same material as the arch or of different material, and may be in the nature of a rib instead of a truss. The trussed frame supports the arch at enough points that it is prevented from distortion due to inequalities of the moduli of elasticity in its various parts, or to other causes, and the arch therefore retains its true form at all stages of loading.

The surfaces of contact between the arch segment 1 and the abutment 4 at one end, also be-- tween segment 2 and abutment 5, and between the two arch segments and the hinge element 3, are all cylindrical surfaces with the axes of the cylinders parallel to the axes of the arch segments, which axes are identical with each other in this case.

These cylindrically shaped bearing surfaces permit free movement of one surface relative to or tensile stresses are set the adjacent one tangentially, so that no shearing up in any part of the arch or abutments. The result is that the arch ring is subjected to purely compressive stresses only, hence can be designed with exact knowledge of the amount of those stresses, is assured of greater safety than an arch with fixed ends, and can be built with the least amount of material for the same factor of safety.

Fig. 2 shows the application of this invention 05 to a multiple arch dam. In this 6 is a shore abutment, '7 and '7 two intermediate abutments or buttresses, 8 and 8 two hinge elements, and 9 and 9 two arch segments in a dam which may have any number of arches. The idea is the same as in the dam of Fig. 1, thedifference being that the hinge element 8 is here designed to combine the thrusts of the two adjacent arch rings and to transmit the resultant load to the buttress 7, giving adjustment and preventing the setting up of any shearing or tensile stresses.

Fig. 3 shows more in detail the construction of the hinge joint, used to permit free movement of the arch segments relative to the hinge members, such as the central part 3 of Fig. 1, or the 30 abutments.

1 and 2 in Fig. 3 represent the ends of segments 1 and 2 of Fig. 1, and 3 represents the central hinge member of Fig. 1. 10 represents a series of cylindrical rods or rollers of suitable size and 5 number bearing against surface plates 11 and 12.

11 and 12 are surface plates, preferably of metal, to transmit and distribute pressure of the rollers to the material of the arch ring or hinge element. The arrangement of parts 10, 11 and 12 between arch ring and hinge element, or between sections of arch rings, or between arch ring and buttress, permits transmission of pressure through the joint, but because of free movement of the rollers prevents transmission of 35 any shearing or cantilever actions. Whenever for any cause the pressures on one side of the center line of the arch ring tend to become greater than on the other side, the rollers 10 turn freely and equalize the pressure. 5100 13 represents asphaltic or other viscous material, filling space between rollers 10 and surface plates 11 and 12, used to prevent leakage of water along the joint and through the dam. 14 represents a flexible seal to prevent passage of 5 water through the hinge.

Fig. 4 is an elevation at section IV-IV of Fig. 2, showing ends of arch segments in contact with abutments, which are shown stepped into the side walls to obtain solid bearing, and {110 obviate danger of slipping and shearing actions.

Fig. 4 shows also that the dam is divided into sections, 9, 9, 9, and 20 by adjustment joints 15 in planes intersecting the axis of the arch, to prevent shearing stresses, flexure or cantilever action between different levels. These joints permit different parts of the dam to deflect according to the water load on them without restriction by adjacent parts. The lowest section of the arch 20 may thus deflect without tending to move the foundation 19 downstream.

Arch reinforcement, as shown in Fig. 1, is not needed where the ratio of length to thickness of arch is not large. It is well known that the strength of a column of given cross section decreases as the slenderness ratio increases, and a limit of slenderness is established which is not exceeded in good engineering practice. A similar rule may be adopted for arches and arched dams.

The stiffening reinforcement need not be ap plied to the arch except where the slenderness ratio requires it. Generally speaking stiffening .of the arch is necessary in the upper parts of a dam, extending down one hundred to one hundred twenty five feet from the top.

The key element 3 corresponds to the keystone of ordinary arches, differing therefrom in having cylindrically shaped sides, so that it acts like .a hinge pin in a hinge and permits deflection of the arch without setting up bending stresses.

Water tightness of dams built according to this invention may be further insuredby the use of flexible seals 14 at the upstream face, covering the adjustment joints and preventing the entrance of water into the joints. Many forms of metallic seals for such a purpose are already known.

This invention has many advantages over the present forms of arches. One of the best known authorities on arch dam design lists sixteen causes of secondary stresses and resulting complication in arch dam calculation. Temperature variation in the concrete, shrinkage due to setting, and swelling due to soaking up by water, are provided for in this invention by movements at the hinges of the arch.

Yielding of the foundation by eccentric vertical loading, .or in a horizontal direction, is prevented by the adjustment planes, which prevent transmission of cantilever stress or horizontal shear to the base.

By movements at the hinged joints it provides for yielding of abutments, which is bound to occur, as certainly as the arch itself yields under loads. If the side wall foundations of a 21am are of different grades of rock, as indicated in Fig. 4, by A, B, and C, the abutments are provided with joints 16 to accommodate yielding of the side wall foundations in varying amounts.

Deformation of the arch at one level of a dam in this invention is uniform, such as results from simple compressive stress only, eliminated practically all secondary stresses, the joints between different levels preventing cantilever and shearing actions. Wedge action is impossible, no matter how thick the arch, because the scientifically correct shaping of the arch hinges compels it to act always as a pure arch.

The description and drawing illustrate the application of this invention to certain forms of arched dams. The invention however is applicable to arches designed for various purposes, and is subject to innumerable variations in proportions and design to suit the various applications.

It maybe noted the cylindrical surfaces at the hinge joints may be curved in the reverse direction; that is, the ends .of the arch element may be convex and the adjacent bearing surfaces of hinges .or abutments concave. .Hinge and adjustment joints may be of either the slip type or roller type, it being held that neither has patentable novelty over the other.

I claim as my invention and desire to secure by Letters Patent the :novel combination of the following elements.

1. In an arched dam, a series of spaced abutments each having a cylindrical socket in its upstream end, arches spanning adjacent abutments having cylindrical sockets in their ends, and cylindrical hinge elements engaging the adjacent sockets of the abutments and arches.

2. In an arch dam,'a series .of spaced abutments each having a cylindrical bearing surface on its upstream end, two-part arches spanning adjacent abutments havingcylindrical socket bearing surfaces in engagement with the cylindrical surfaces of the abutments, the points of contact of the two parts of the arches having cylindrical sockets, and a cylindrical hinge element engaging said sockets.

3. In an arch dam, a series of spaced abut- ;ments each having cylindrical bearing surfaces on its upstream end, a plurality of vertically stacked arches spanning adjacent abutments and separated from the base by adjustment joints in planes intersecting the axis, and each having cylindrical socket bearing surfaces on its ends in engagement with corresponding cylindrical bearing surfaces of the abutments.

CHARLES C. TILLOTSON. 

